igneous
Granite pebble
Granite; primarily quartz, feldspar, and mica
AI-generated identification · may be incorrectCoarse-grained, speckled gray-and-white rock with a granular texture and subrounded natural or tumbled surface. Hardness is about 6–7 Mohs; vitreous quartz and feldspar luster, no obvious cleavage at specimen scale, and specific gravity about 2.63–2.75.
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Physical properties
Coarse-grained, speckled gray-and-white rock with a granular texture and subrounded natural or tumbled surface. Hardness is about 6–7 Mohs; vitreous quartz and feldspar luster, no obvious cleavage at specimen scale, and specific gravity about 2.63–2.75.
Formation & geological history
Slow cooling and crystallization of silica-rich magma deep in the continental crust, commonly during Precambrian to Phanerozoic plutonic events; later exposed by uplift and erosion.
Uses & applications
Used extensively as dimension stone, countertops, paving, monuments, aggregate, and landscaping rock; small attractive pieces are collected but generally have low gem value.
Geological facts
The white crystals are commonly plagioclase or potassium feldspar, dark grains are biotite or amphibole, and translucent grains may be quartz. Its visible interlocking crystals distinguish it from many fine-grained volcanic rocks.
Field identification & locations
Identify it by its randomly interlocking gray, white, and black crystals, hardness, and lack of layering or foliation; common worldwide in continental mountain belts and glacial deposits.
